This invention relates to monitoring systems which detect the compaction of soil in backfilled excavations.
Excavations such as utility trenches, foundations and the like are generally backfilled in layers known as lifts. Each lift of backfill material is compacted before the addition of the next lift. If the backfill material is improperly compacted, or if an unsuitable backfill material is used, the backfilled excavation may subside. Subsidence under a foundation, roadway or other structure can lead to costly repairs.
U.S. Pat. No. 5,105,650 to Atkinson et al., which is assigned to the assignee of this application and is incorporated by reference herein, discloses an apparatus for monitoring the compaction of soil which includes a hammer for delivering impact energy to soil material and a piezoelectric sensor at the bottom of the backfilled region for monitoring the amount of impact energy delivered to the backfill. The sensor transmits electrical signals representing the received impact energy to a control module which analyzes these signals to determine when satisfactory compaction is achieved.